Fin isolation structures of semiconductor devices

ABSTRACT

A method of forming a fin field effect transistor (finFET) on a substrate includes forming a fin structure on the substrate and forming a shallow trench isolation (STI) region on the substrate. First and second fin portions of the fin structure extend above a top surface of the STI region. The method further includes oxidizing the first fin portion to convert a first material of the first fin portion to a second material. The second material is different from the first material of the first fin portion and a material of the second fin portion. The method further includes forming an oxide layer on the oxidized first fin portion and the second fin portion and forming first and second polysilicon structures on the oxide layer.

This application is a continuation application of U.S. patentapplication Ser. No. 16/204,892, titled “Fin Isolation Structures ofSemiconductor Devices,” filed on Nov. 29, 2018, which is a divisionalapplication of U.S. patent application Ser. No. 15/718,752, titled “FinIsolation Structures of Semiconductor Devices,” filed on Sep. 28, 2017(U.S. Pat. No. 10,714,394), all of which are incorporated herein byreference in their entireties.

BACKGROUND

With advances in semiconductor technology, there has been increasingdemand for higher storage capacity, faster processing systems, higherperformance, and lower costs. To meet these demands, the semiconductorindustry continues to scale down the dimensions of semiconductordevices, such as metal oxide semiconductor field effect transistors(MOSFETs), including planar MOSFETs and fin field effect transistors(finFETs). Such scaling down has increased the complexity ofsemiconductor manufacturing processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of this disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the common practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is an isometric view of fin field effect transistors (finFETs),in accordance with some embodiments.

FIGS. 2A-2C are cross-sectional views of finFETs, in accordance withsome embodiments.

FIGS. 3A-3C are cross-sectional views of finFETs, in accordance withsome embodiments.

FIG. 4 is a flow diagram of a method for fabricating finFETs, inaccordance with some embodiments.

FIGS. 5-14 are isometric views of finFETs at various stages of theirfabrication process, in accordance with some embodiments.

Illustrative embodiments will now be described with reference to theaccompanying drawings. In the drawings, like reference numeralsgenerally indicate identical, functionally similar, and/or structurallysimilar elements.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over a second feature in the description that followsmay include embodiments in which the first and second features areformed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Asused herein, the formation of a first feature on a second feature meansthe first feature is formed in direct contact with the second feature.In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition does not in itselfdictate a relationship between the various embodiments and/orconfigurations discussed.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper,” and the like may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. The spatially relative termsare intended to encompass different orientations of the device in use oroperation in addition to the orientation depicted in the figures. Theapparatus may be otherwise oriented (rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein maylikewise be interpreted accordingly.

Fins of fin field effect transistors (finFETs) may be patterned by anysuitable method. For example, the fins may be patterned using one ormore photolithography processes, including double-patterning ormulti-patterning processes. Double-patterning or multi-patterningprocesses can combine photolithography and self-aligned processes,allowing patterns to be created that have, for example, pitches smallerthan what is otherwise obtainable using a single, directphotolithography process. For example, in some embodiments , asacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

It is noted that references in the specification to “one embodiment,”“an embodiment,” “an example embodiment,” “exemplary,” etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases do not necessarily refer to the same embodiment. Further,when a particular feature, structure or characteristic is described inconnection with an embodiment, it would be within the knowledge of oneskilled in the art to effect such feature, structure or characteristicin connection with other embodiments whether or not explicitlydescribed.

It is to be understood that the phraseology or terminology herein is forthe purpose of description and not of limitation, such that theterminology or phraseology of the present specification is to beinterpreted by those skilled in relevant art(s) in light of theteachings herein.

As used herein, the term “selectivity” refers to the ratio of the etchrates of two materials under the same etching conditions.

As used herein, the term “about” indicates the value of a given quantitythat can vary based on a particular technology node associated with thesubject semiconductor device. Based on the particular technology node,the term “about” can indicate a value of a given quantity that varieswithin, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±30% ofthe value).

As used herein, the term “substantially” indicates the value of a givenquantity varies by ±5% of the value.

As used herein, the term “substrate” describes a material onto whichsubsequent material layers are added. The substrate itself may bepatterned. Materials added on top of the substrate may be patterned ormay remain unpatterned. Furthermore, the substrate may be a wide arrayof semiconductor materials such as, for example, silicon, germanium,gallium arsenide, indium phosphide, etc. Alternatively, the substratemay be made from an electrically non-conductive material such as, forexample, a glass or a sapphire wafer.

As used herein, the term “high-k” refers to a high dielectric constant.In the field of semiconductor device structures and manufacturingprocesses, high-k refers to a dielectric constant that is greater thanthe dielectric constant of SiO₂ (e.g., greater than 3.9).

As used herein, the term “low-k” refers to a small dielectric constant.In the field of semiconductor device structures and manufacturingprocesses, low-k refers to a dielectric constant that is less than thedielectric constant of SiO₂ (e.g., less than 3.9).

As used herein, the term “p-type” defines a structure, layer, and/orregion as being doped with p-type dopants, such as, for example, boron.

As used herein, the term “n-type” defines a structure, layer, and/orregion as being doped with n-type dopants, such as, for example,phosphorus.

As used herein, the term “vertical” means nominally perpendicular to thesurface of a substrate.

As used herein, the term “critical dimension” refers to the smallestfeature size (e.g., line width) of a finFET and/or an element of anintegrated circuit.

This disclosure provides example methods for fabricating fin isolationstructures of finFETs with fewer process steps than other methods usedin forming fin isolation structures. The example methods may form thefin isolation structures without substantially degrading the structuralintegrity of fin structures adjacent to and/or in contact with the finisolation structures. In some embodiments, the example methods may formthe fin isolation structures without substantially reducing strain inthe fin structures and without adversely affecting the high mobilitychannel performance of the finFETs.

FIG. 1 is an isometric view of a device 100 having first and secondfinFETs 100A and 100B, according to some embodiments. The discussionbelow of elements of finFET 100A applies to elements of finFET 100B withthe same annotations unless mentioned otherwise. It will be recognizedthat the view of device 100 is shown for illustration purposes and maynot be drawn to scale.

In some embodiments, finFETs 100A and 100B may be formed on a substrate102. In some embodiments, finFETs 100A and 100B may each include shallowtrench isolation (STI) regions 104, fin structures 106, fin isolationstructures 107, epitaxial regions 108, gate structures 110, spacers 120,etch stop layer (ESL) 122, and interlayer dielectric (ILD) layer 124.Even though FIG. 1 shows finFETs 100A and 100B each having one finisolation structure 107, finFETs 100A and 100B may have one or more finisolation structures similar to fin isolation structures 107. In someembodiments, finFETs 100A and 100B may be either n-type finFETs orp-type finFETs. In some embodiments, finFETs 100A and 100B may be n- andp-type finFETs, respectively, or p- and n-type finFETs, respectively.

Substrate 102 may be a physical material on which finFET 100 are formed.Substrate 102 may be a semiconductor material such as, but not limitedto, silicon. In some embodiments, substrate 102 includes a crystallinesilicon substrate (e.g., wafer). In some embodiments, substrate 102includes (i) an elementary semiconductor, such as germanium; (ii) acompound semiconductor including silicon carbide, gallium arsenide,gallium phosphide, indium phosphide, indium arsenide, and/or indiumantimonide; (iii) an alloy semiconductor including silicon germaniumcarbide, silicon germanium, gallium arsenic phosphide, gallium indiumphosphide, gallium indium arsenide, gallium indium arsenic phosphide,aluminum indium arsenide, and/or aluminum gallium arsenide; or (iv) acombination thereof. Further, substrate 102 may be doped depending ondesign requirements (e.g., p-type substrate or n-type substrate). Insome embodiments, substrate 102 may be doped with p-type dopants (e.g.,boron, indium, aluminum, or gallium) or n-type dopants (e.g., phosphorusor arsenic).

STI regions 104 may provide electrical isolation to finFETs 100A and100B from each other and from neighboring active and passive elements(not illustrated herein) integrated with or deposited onto substrate102. STI regions 104 may be made of a dielectric material. In someembodiments, STI regions 104 may include silicon oxide, silicon nitride,silicon oxynitride, fluorine-doped silicate glass (FSG), a low-kdielectric material, and/or other suitable insulating material. In someembodiments, STI regions 104 may include a multi-layered structure.

Fin structures 106 may traverse along a Y-axis and through gatestructures 110. Portions of fin structures 106 extending above STIregions 104 may be wrapped around by gate structures 110 (not shown inFIG. 1; shown in FIGS. 2B and 3B). In some embodiments, fin structures106 may each include material similar to substrate 102. In someembodiments, fin portions 106A and 106B of each fin structures 106 mayinclude material similar to or different from each other. In someembodiments, fin portions 106A and 106B of p-type finFETs 100A and 100Bmay include material different from each other. In some embodiments, finportions 106A and 106B of n-type finFETs 100A and 100B may includematerial similar to each other. In some embodiments, fin portions 106Amay include an alloy semiconductor including silicon germanium carbide,silicon germanium, gallium arsenic phosphide, gallium indium phosphide,gallium indium arsenide, gallium indium arsenic phosphide, aluminumindium arsenide, and/or aluminum gallium arsenide and fin portions 106Bmay include an elementary semiconductor, such as silicon or germanium.Fin portions 106A and 106B may be positioned above and below topsurfaces of STI regions 104, respectively. In some embodiments, topsurfaces of fin portions 106A may be substantially coplanar with topsurfaces of STI regions. In some embodiments, fin portions 106A and 106Bmay each have a height ranging from about 50 nm to about 60 nm.

In some embodiments, fin structures 106 may each be formed from aphotolithographic patterning and an etching of respective substrate 102.Fin structures 106 may have widths W in a range from about 5 nm to about10 nm, according to some embodiments. Other widths and materials for finstructures 106 are within the scope and spirit of this disclosure.

In some embodiments, epitaxial regions 108 may be grown on fin portionsof fin structures 106 that extend above STI regions 104 and are notunderlying gate structures 110. In some embodiments, epitaxial regions108 may be grown on areas of fin portions 106A that are not underlyinggate structures 110. Epitaxial regions 108 may include anepitaxially-grown semiconductor material. In some embodiments, theepitaxially grown semiconductor material is the same material as thematerial of substrate 102. In some embodiments, the epitaxially-grownsemiconductor material includes a different material from the materialof substrate 102. The epitaxially-grown semiconductor material mayinclude: (i) a semiconductor material such as, for example, germanium orsilicon; (ii) a compound semiconductor material such as, for example,gallium arsenide and/or aluminum gallium arsenide; or (iii) asemiconductor alloy such as, for example, silicon germanium and/orgallium arsenide phosphide. In some embodiments, epitaxial regions 108may each have a thickness 108 t in a range from about 5 nm to about 15nm around respective portions of fin structures 106 above STI regions104.

In some embodiments, epitaxial regions 108 may be grown by (i) chemicalvapor deposition (CVD) such as, for example, by low pressure CVD(LPCVD), atomic layer CVD (ALCVD), ultrahigh vacuum CVD (UHVCVD),reduced pressure CVD (RPCVD), or any suitable CVD; (ii) molecular beamepitaxy (MBE) processes; (iii) any suitable epitaxial process; or (iv) acombination thereof. In some embodiments, epitaxial regions 108 may begrown by an epitaxial deposition/partial etch process, which repeats theepitaxial deposition/partial etch process at least once. Such repeateddeposition/partial etch process is also called a “cyclic deposition-etch(CDE) process.” In some embodiments, epitaxial regions 108 may be grownby selective epitaxial growth (SEG), where an etching gas is added topromote the selective growth of semiconductor material on the exposedsurfaces of fin structures 108, but not on insulating material (e.g.,dielectric material of STI regions 104).

In some embodiments, epitaxial regions 108 may be p-type or n-type. Insome embodiments, epitaxial regions 108 of finFETs 100A and 100B may beof opposite doping type with respect to each other. In some embodiments,p-type epitaxial regions 108 may include SiGe and may be in-situ dopedduring an epitaxial growth process using p-type dopants such as, forexample, boron, indium, or gallium. For p-type in-situ doping, p-typedoping precursors such as, but not limited to, diborane (B₂H₆), borontrifluoride (BF₃), and/or other p-type doping precursors can be used.

In some embodiments, each of p-type epitaxial regions 108 may have aplurality of sub-regions (not shown) that may include SiGe and maydiffer from each other based on, for example, doping concentration,epitaxial growth process conditions, and/or relative concentration of Gewith respect to Si. In some embodiments, each of the sub-regions mayhave thicknesses similar to or different from each other and thicknessesmay range from about 0.5 nm to about 5 nm. In some embodiments, theatomic percent Ge in sub-regions closest to a top surface of finstructures 106 may be smaller than the atomic percent Ge in sub-regionsfarthest from the top surface of fin structures 106. In someembodiments, the sub-regions closest to the top surface of finstructures 106 may include Ge in a range from about 15 atomic percent toabout 35 atomic percent, while the sub-regions farthest from the topsurface of fin structures 106 may include Ge in a range from about 25atomic percent to about 50 atomic percent with any remaining atomicpercent being Si in the sub-regions.

The plurality of sub-regions of p-type epitaxial regions 108 may beepitaxially grown under a pressure of about 10 Torr to about 300 Torrand at a temperature of about 500° C. to about 700° C. using reactiongases such as HCl as an etching agent, GeH₄ as Ge precursor,dichlorosilane (DCS) and/or SiH₄ as Si precursor, B₂H₆ as B dopantprecursor, H₂, and/or N₂. To achieve different concentration of Ge inthe plurality of sub-regions, the ratio of a flow rate of Ge to Siprecursors may be varied during their respective growth process,according to some embodiments. For example, a Ge to Si precursor flowrate ratio in a range from about 9 to about 25 may be used during theepitaxial growth of the sub-regions closest to the top surface of finstructures 106, while a Ge to Si precursor flow rate ratio less thanabout 6 may be used during the epitaxial growth of the sub-regionsfarthest from the top surface of fin structures 106.

The plurality of sub-regions of p-type epitaxial regions 108 may havevarying p-type dopant concentration with respect to each other,according to some embodiments. For example, the sub-regions closest tothe top surface of fin structures 106 may be undoped or may have adopant concentration lower (e.g., dopant concentration less than about8×10²⁰ atoms/cm³) than the dopant concentrations (e.g., dopantconcentration in a range from about 1×10²⁰ to about 3×10²² atoms/cm³) ofthe sub-regions farthest from the top surface of fin structures 106.

In some embodiments, n-type epitaxial regions 108 may include Si and maybe in-situ doped during an epitaxial growth process using n-type dopantssuch as, for example, phosphorus or arsenic. For n-type in-situ doping,n-type doping precursors such as, but not limited to, phosphine (PH₃),arsine (AsH₃), and/or other n-type doping precursor can be used. In someembodiments, each of n-type epitaxial regions 108 may have a pluralityof n-type sub-regions. Except for the type of dopants, the plurality ofn-type sub-regions may be similar to the plurality of p-typesub-regions, in thickness, relative Ge concentration with respect to Si,dopant concentration, and/or epitaxial growth process conditions.

Other materials, thicknesses, Ge concentrations, and dopantconcentrations for the plurality of n-type and/or p-type sub-regions arewithin the scope and spirit of this disclosure.

Fin structures 106 are current-carrying structures for respectivefinFETs 100A and 100B. Epitaxial regions 108 along with the portions offin structures 106 covered by respective epitaxial regions 106 areconfigured to function as source/drain (S/D) regions of respectivefinFETs 100A and 100B. Channel regions (not shown) of finFETs 100A and100B may be formed in portions of their respective fin structures 106underlying gate structures 110.

In some embodiments, fin isolation regions 107 may be electricallyinsulated portions of fin structures 106. Fin isolation structures 107may be also referred as “electrically inactive regions of fin structures106 or finFETs 100A and/or 100B.” In some embodiments, fin isolationstructures 107 may be used to reduce active regions of finFETs 100A and100B to reduce power consumption. Fin isolation structures 107 may bepositioned between and/or in contact with two electrically activeportions of fin structures 106 (not shown in FIG. 1; shown in FIG. 11).In some embodiments, portions of fin structures 106 that areelectrically conductive and/or function as S/D regions may be referredas “electrically active portions of fin structures 106.” In someembodiments, fin isolation structures 107 may have horizontal andvertical dimensions (e.g., width and height) that are substantiallyequal to that of fin portions 106A. In some embodiments, fin isolationstructures 107 may have a vertical dimension that is smaller thanvertical dimensions of fin portions 106A (discussed further withreference to FIGS. 3A-3C). In some embodiments, fin isolation structuresmay include oxide material such as, for example, silicon oxide orsilicon germanium oxide. In some embodiments, fin isolation structures107 may include doped oxide material such as, for example, doped SiO₂having Ge dopants.

One or more portions of fin structures 106 that extend above STI regionsmay be selectively modified (e.g., converted and/or oxidized) to anelectrically insulating structure to form fin isolation structures 107.Such selective conversion of the one or more portions of fin structures106 may be done by using photolithographic patterning to expose the oneor more portions and performing an oxidation process on the exposedportions. In order to form fin isolation structures 107, the one or moreportions of fin structures 106 are not removed by an etching process(also referred as a “fin cutting process”) and replaced with a depositedinsulating material as done in other methods of forming fin isolationstructures. This removal process performed in other methods reducestrain in fin structures 106 when finFETs 100A and 100B may be used asp-type finFETs having strained fin structures 106. Such reduction instrain may adversely affect high mobility channel performance offinFETs. Thus, the example methods of forming fin isolation structures107 in the present disclosure, without the use of fin cutting process,may prevent the reduction of strain in fin structures 106, andconsequently, improve the performance of finFETs 100A and 100B. Theformation of fin isolation structures 107 is described in further detailwith reference to FIGS. 5-11.

Each of gate structures 110 may include a dielectric layer (not shown)and a gate electrode 118. Additionally, in some embodiments, each ofgate structures 110 may include an oxide layer 114 and may form a partof gate dielectric layers of gate structures 110 when finFETs 100A and100B are used as input/output (IO) devices in peripheral circuits (e.g.,IO circuits) formed in peripheral regions (also may be referred as “IOregions” or “high voltage regions”) of an integrated circuit (IC). TheIO devices may be configured to handle the input/outputvoltages/currents of the IC and to tolerate a greater amount of voltageor current swing than non-IO devices.

In some embodiments, oxide layer 114 may be absent when finFETs 100A and100B are used as non-input/output (non-IO) devices in core circuits(also may be referred as “logic circuits” or “memory circuits”) formedin core regions (also may be referred as “logic regions” or “memoryregions”) of an IC. In some embodiments, the non-IO devices may be coredevices, logic devices, and/or memory devices that are not configured tohandle the input/output voltages/currents directly. In some embodiments,the non-IO devices may include logic gates such as, for example, NAND,NOR, INVERTER, or a combination thereof. In some embodiments, the non-IOdevices may include a memory device such as, for example, a staticrandom-access memory (SRAM) device.

Referring back to FIG. 1, the dielectric layer may be adjacent to and incontact with gate electrode 118. The dielectric layer may have athickness in a range of about 1 nm to about 5 nm. The dielectric layermay include silicon oxide and may be formed by CVD, atomic layerdeposition (ALD), physical vapor deposition (PVD), e-beam evaporation,or other suitable process. In some embodiments, dielectric layer mayinclude (i) a layer of silicon oxide, silicon nitride, and/or siliconoxynitride, (ii) a high-k dielectric material such as, for example,hafnium oxide (HfO₂), titanium oxide (TiO₂), hafnium zirconium oxide(HfZrO), tantalum oxide (Ta₂O₃), hafnium silicate (HfSiO₄), zirconiumoxide (ZrO₂), zirconium silicate (ZrSiO₂), (iii) a high-k dielectricmaterial having oxides of lithium (Li), beryllium (Be), magnesium (Mg),calcium (Ca), strontium (Sr), scandium (Sc), yttrium (Y), zirconium(Zr), aluminum (Al), lanthanum (La), cerium (Ce), praseodymium (Pr),neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium(Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), or lutetium (Lu), or (iv) a combination thereof. High-kdielectric layers may be formed by ALD and/or other suitable methods. Insome embodiments, dielectric layer may include a single layer or a stackof insulating material layers. Other materials and formation methods fordielectric layer are within the scope and spirit of this disclosure.

In some embodiments, oxide layer 114 may be in contact with spacers 120and may extend along a Y-axis in a manner such that a portion of oxidelayer may be under and in contact with dielectric layer and anotherportion of oxide layer 114 may be under and in contact with spacers 120Aas shown in FIG. 1. Oxide layer 114 may include a suitable oxidematerial, such as, for example, silicon oxide and may be deposited usinga suitable deposition process, such as, for example, CVD or ALD. In someembodiments, oxide layer 114 may have a thickness 114 t ranging fromabout 1 nm to about 3 nm. It will be recognized that other oxidematerials, formation methods, and thicknesses for protective oxide layer114 are within the scope and spirit of this disclosure.

Gate electrode 118 may include a gate work function metal layer (notshown) and a gate metal fill layer (not shown). In some embodiments, thegate work function metal layer is disposed on dielectric layer 116. Thegate work function metal layer may include a single metal layer or astack of metal layers. The stack of metal layers may include metalshaving work functions similar to or different from each other. In someembodiments, the gate work function metal layer may include, forexample, aluminum (Al), copper (Cu), tungsten (W), titanium (Ti),tantalum (Ta), titanium nitride (TiN), tantalum nitride (TaN), nickelsilicide (NiSi), cobalt silicide (CoSi), silver (Ag), tantalum carbide(TaC), tantalum silicon nitride (TaSiN), tantalum carbon nitride (TaCN),titanium aluminum (TiAl), titanium aluminum nitride (TiAlN), tungstennitride (WN), metal alloys, and/or combinations thereof. The gate workfunction metal layer may be formed using a suitable process such as ALD,CVD, PVD, plating, or combinations thereof. In some embodiments, thegate work function metal layer has a thickness in a range from about 2nm to about 15 nm. Based on the disclosure herein, it will be recognizedthat other materials, formation methods and thicknesses for the gatework function metal layer are within the scope and spirit of thisdisclosure.

The gate metal fill layer may include a single metal layer or a stack ofmetal layers. The stack of metal layers may include metals differentfrom each other. In some embodiments, the gate metal fill layer mayinclude a suitable conductive material such as, for example, Ti, silver(Ag), Al, titanium aluminum nitride (TiAlN), tantalum carbide (TaC),tantalum carbo-nitride (TaCN), tantalum silicon nitride (TaSiN),manganese (Mn), Zr, titanium nitride (TiN), tantalum nitride (TaN),ruthenium (Ru), molybdenum (Mo), tungsten nitride (WN), copper (Cu),tungsten (W), cobalt (Co), nickel (Ni), titanium carbide (TiC), titaniumaluminum carbide (TiAlC), tantalum aluminum carbide (TaAlC), metalalloys, and/or combinations thereof. The gate metal fill layer may beformed by ALD, PVD, CVD, or other suitable deposition process. Based onthe disclosure herein, it will be recognized that other materials andformation methods for the gate metal fill layer are within the scope andspirit of this disclosure.

Spacers 120 may form sidewalls of gate structures 110 and are in contactwith oxide layer 114 and in contact with dielectric layer, according tosome embodiments. Spacers 120 may include insulating material such as,for example, silicon oxide, silicon nitride, a low-k material, or acombination thereof. Spacers 120 may have a low-k material with adielectric constant less than 3.9 (e.g., less than 3.5, 3.0, or 2.8). Insome embodiments, each of spacers 120 may have a thickness ranging fromabout 7 nm to about 10 nm. Other materials and thicknesses for spacers120 are within the scope and spirit of this disclosure.

ESL 122 may be configured to protect gate structures 110 and/or portionsof epitaxial regions 108 that are not in contact with metal silicidelayers 129 and/or source/drain (S/D) contact structures 128. Thisprotection may be provided, for example, during formation of ILD layer124 and/or S/D contact structures 128. ESL 122 may be disposed on sidesof spacers 120. In some embodiments, ESL 122 may include, for example,silicon nitride (SiN_(x)), silicon oxide (SiO_(x)), silicon oxynitride(SiON), silicon carbide (SiC), silicon carbo-nitride (SiCN), boronnitride (BN), silicon boron nitride (SiBN), silicon carbon boron nitride(SiCBN), or a combination thereof. In some embodiments, ESL 122 mayinclude silicon nitride or silicon oxide formed by low pressure chemicalvapor deposition (LPCVD), plasma enhanced chemical vapor deposition(PECVD), chemical vapor deposition (CVD), or silicon oxide formed by ahigh-aspect-ratio process (HARP). In some embodiments, ESL 122 may havea thickness in a range from about 3 nm to 10 nm or from about 10 nm toabout 30 nm. Other materials, formation methods, and thicknesses for ESL122 are within the scope and spirit of this disclosure.

ILD layer 124 may be disposed on ESL 122 and may include a dielectricmaterial deposited using a deposition method suitable for flowabledielectric materials (e.g., flowable silicon oxide, flowable siliconnitride, flowable silicon oxynitride, flowable silicon carbide, orflowable silicon oxycarbide). For example, flowable silicon oxide may bedeposited using flowable CVD (FCVD). In some embodiments, the dielectricmaterial is silicon oxide. In some embodiments, ILD layer 124 may have athickness in a range from about 50 nm to about 200 nm. Other materials,thicknesses, and formation methods for ILD layer 124 are within thescope and spirit of this disclosure.

S/D contact structures 128 may be configured to electrically connectepitaxial regions 108 to other elements of finFETs 100A and 100B and/orof the integrated circuit. S/D contact structures 128 may be formedwithin ILD layer 124. Each of S/D contact structures 128 may include ametal silicide layer 129 and a conductive region 132. The metal silicidelayers 129 may be at interface between top surfaces of epitaxial regions108 and conductive regions 132. In some embodiments, there may beconductive liners (not shown) between metal silicide layers 129 andconductive regions 132. The conductive liners may be configured asdiffusion barriers to prevent diffusion of unwanted atoms and/or ionsinto epitaxial regions 108 during formation of conductive regions 132.In some embodiments, the conductive liners may include a single layer ora stack of conductive materials such as, for example, TiN, Ti, Ni, TaN,Ta, or a combination thereof. In some embodiments, the conductive linersmay act as an adhesion-promoting-layer, a glue-layer, a primer-layer, aprotective-layer, and/or a nucleation-layer. The conductive liners mayhave a thickness in a range from about 1 nm to about 2 nm, according tosome embodiments.

In some embodiments, metal silicide layers 129 may include metalsilicides and may provide a low resistance interface between respectiveconductive regions 132 and corresponding epitaxial regions 108. Examplesof metal used for forming the metal silicides are Co, Ti, or Ni.

In some embodiments, conductive regions 132 may include conductivematerials such as, for example, W, Al, or Co. In some embodiments,conductive regions 132 may each have an average horizontal dimension(e.g., width) in a range from about 15 nm to about 25 nm and may eachhave an average vertical dimension (e.g., height) in a range from about400 nm to about 600 nm. Other materials and dimensions for conductiveliners, metal silicide layers 129, and conducive regions 132 are withinthe scope and spirit of this disclosure.

In some embodiments, finFETs 100A and 100B may further include aninsulating liner 126 deposited along the sidewalls of fin portions 106Band a top surface of substrate 102. Insulating liner 126 may be formedto protect fin structures 106 from oxidation during formation of STIregions 104. The formation and function of insulating liner 126 isfurther discussed with reference to FIGS. 6-7. In some embodiments,insulating liner 126 may include nitride (e.g., SiN) or oxide (e.g.,SiO₂) materials.

FIG. 1 shows four gate structures 110. However, it will be recognizedthat finFETs 100A and 100B may have one or more gate structures similarand/or parallel to gate structures 110. In addition, finFETs 100A and100B may be incorporated into an integrated circuit through the use ofother structural components such as gate contact structures, conductivevias, conductive lines, dielectric layers, passivation layers, etc.,that are omitted for the sake of simplicity. It will be recognized thatcross-sectional shapes of STI regions 104, fin structures 106, finisolation structures 107, epitaxial regions 108, gate structures 110,spacers 120, ESL 124, ILD layer 126, and S/D contact structures 128 areillustrative and are not intended to be limiting.

FinFETs 100A and 100B are further described with reference to FIGS.2A-2C. Elements in FIGS. 2A-2C with the same annotations as elements inFIG. 1 are described above. FIGS. 2A-2C are cross-sectional views alonglines A-A, B-B, and C-C of device 100 of FIG. 1, respectively, accordingto some embodiments. It will be recognized that the views of finFETs100A and 100B in FIGS. 2A-2C are shown for illustration purposes and maynot be drawn to scale. It will be recognized that cross-sectional shapesof STI regions 104, fin structures 106, fin isolation structures 107,epitaxial regions 108, gate structures 110, spacers 120, ESL 122, ILDlayer 124, and S/D contact structures 128 shown in FIGS. 2A-2C areillustrative and are not intended to be limiting.

As shown in FIGS. 2A-2B, some portions of fin isolation structures 107may be wrapped around with ESL 122 and ILD layer 124 and some portionsmay be wrapped around with oxide layer 114 and gate electrode 118,respectively. In some embodiments, cross-sections of fin isolationstructure 107 may each have a vertical dimension 107 t that issubstantially equal to vertical dimensions 106At of fin portions 106A.In some embodiments, dimension 107 t may range from about 50 nm to about60 nm. In some embodiments, the cross-sections of fin isolationstructures 107 may each have a horizontal dimension 107 w that issubstantially equal to horizontal dimensions 106Aw of fin portions 106A.In some embodiments, dimension 107 w may range from about 5 nm to about10 nm.

In some embodiments, fin isolation structure 107 may have an interface107 s. Interface 107 s may be formed as a result of oxidation processthat may be used to form fin isolation structure 107. In someembodiments, interface 107 s may have high concentration of dopants(e.g., Ge dopants), which may be as a result of the oxidation process.The formation of interface 107 s is further discussed below withreference to FIG. 11.

FIG. 2C shows a cross-sectional view of device 100 along line C-Crunning through one of fin structures 106 having a fin isolationstructure 107. It will be understood that based on design and functionof device 100, one or more of fin structures 106 may each have one ormore fin isolation structures 107. As shown in FIG. 2C, fin isolationstructure 107 may be adjacent to fin portion 106A along a Y-axis and maybe on top of fin portion 106B. Some portions of fin isolation structure107 may be under gate structures 110 and some portions of fin isolationstructure 107 may be under ESL 122 and ILD layer 124, as shown in FIG.2C. In some embodiments, S/D contact structures 128 may not be formed onfin isolation structures 107 and may be formed on epitaxial regions 108.FIG. 2C shows vertical dimension 107 t may be substantially equal tovertical dimension 106At.

FinFETs 100A and 100B are further described with reference to FIGS.3A-3C. Elements in FIGS. 3A-3C with the same annotations as elements inFIGS. 1 and 2A-2B are described above. The discussion of elements ofFIGS. 1 and 2A-2B applies to elements of FIGS. 3A-3C unless mentionedotherwise. FIGS. 3A-3C are cross-sectional views along lines A-A, B-B,and C-C of device 100 of FIG. 1, respectively, according to someembodiments. It will be recognized that the views of finFETs 100A and100B in FIGS. 3A-3C are shown for illustration purposes and may not bedrawn to scale. It will be recognized that cross-sectional shapes of STIregions 104, fin structures 106, fin isolation structures 107, epitaxialregions 108, gate structures 110, spacers 120, ESL 122, ILD layer 124,and S/D contact structures 128 shown in FIGS. 3A-3C are illustrative andare not intended to be limiting.

As shown in FIGS. 3A-3B, some portions of fin isolation structures 107may be wrapped around with ESL 122 and ILD layer 124 and some portionsmay be wrapped around with oxide layer 114 and gate electrode 118,respectively. In some embodiments, cross-sections of fin isolationstructures 107 under ILD layer 124 may each have a vertical dimension107 t ₁* that is smaller than vertical dimensions 106At of fin portions106A, as shown in FIG. 3A. In some embodiments, dimension 107 t ₁* mayrange from about 40 nm to about 50 nm. In some embodiments,cross-sections of fin isolation structures 107 under gate structures 110may each have a vertical dimension 107 t ₂* that is smaller thanvertical dimensions 106At of fin portions 106A, as shown in FIG. 3B. Insome embodiments, dimension 107 t ₂* may range from about 40 nm to about50 nm. In some embodiments, dimensions 107 t ₁* and 107 t ₂* may beequal to or different from each other.

In some embodiments, the cross-sections of fin isolation structures 107under ILD layer 124 and gate structures 110 may each have a horizontaldimension that varies along a Z-axis. For example, as shown in FIGS.3A-3B, horizontal dimensions of fin isolation structures 107 under ILDlayer 124 and gate structure 110 gradually becomes smaller from bases107 b towards peaks 107 a of fin isolation structures 107. In someembodiments, horizontal dimension at bases 107 b of fin isolationstructures may be substantially equal to horizontal dimensions 106Aw offin portions 106A.

FIG. 3C shows a cross-sectional view of device 100 along line C-Crunning through one of fin structures 106 having a fin isolationstructure 107, according to some embodiments. As shown in FIG. 3C, finisolation structure 107 may be adjacent to fin portion 106A along aY-axis and may be on top of fin portion 106B. Further shown in FIG. 3C,a cross-section of fin isolation structure 107 along a Y-axis may havevarying vertical dimensions. For example, the cross-section of finisolation structure 107 along a Y-axis may have a first verticaldimension 107 t ₃* under ILD layer 124 and may have a second verticaldimension 107 t ₄* that may be different from 107 t ₃*. In someembodiments, vertical dimensions 107 t ₁*, 107 t ₂*, 107 t ₃*, and 107 t₄* may be equal to or different from each other and may be smaller thandimensions 106At of fin portions 106A.

FIG. 4 is a flow diagram of an example method 400 for fabricating device100 as described with reference to FIGS. 1, 2A-2B, and 3A-3B, accordingto some embodiments. For illustrative purposes, the operationsillustrated in FIG. 4 will be described with reference to the examplefabrication process for fabricating device 100 as illustrated in FIGS.5-14. FIGS. 5-14 are isometric views of device 100 at various stages ofits fabrication, according to some embodiments. Operations can beperformed in a different order or not performed depending on specificapplications. It should be noted that method 400 does not producecomplete device 100. Accordingly, it is understood that additionalprocesses may be provided before, during, and after method 400, and thatsome other processes may only be briefly described herein. Elements inFIGS. 5-11 with the same annotations as elements in FIGS. 1, 2A-2C, and3A-3C are described above.

In operation 405, fin structures of first and second finFETs are formedon a substrate. For example, as shown in FIG. 5, fin structures 106 offinFETs 100A and 100B are formed on substrate 102. The formation of finstructures 106 may include (i) epitaxially growing a layer of SiGe onunetched substrate 102, (ii) patterning a hard mask layer on theepitaxial layer of SiGe to form a patterned hard mask layer 534, and(iii) etching the epitaxial layer of SiGe and substrate 102 throughpatterned hard mask layer 534. The etching may be performed using, forexample, a dry etch process, a wet etch process, or a combinationthereof. The dry etch process may use reactive ion etching using achlorine or fluorine based etchant. In some embodiments, the hard masklayer may be a thin film including silicon oxide formed, for example,using a thermal oxidation process. In some embodiments, hard mask layermay be formed of silicon nitride using, for example, low pressurechemical vapor deposition (LPCVD) or plasma enhanced CVD (PECVD). Insome embodiments, fin portions 106A having SiGe may have a verticaldimension ranging from about 50 nm to about 60 nm and fin portions 106Bmay have a vertical dimension ranging from about 50 nm to about 60 nm.In some embodiments, fin structures 106 may have a horizontal dimensionranging from about 5 nm to about 10 nm.

In referring to FIG. 4, in operation 410, STI regions are formed on thesubstrate. For example, STI regions 104 may be formed as described withreference to FIGS. 6-7. The formation of STI regions 104 may includedepositing a protective layer 636* (shown in FIG. 6) on the structure ofFIG. 5 to form the structure shown in FIG. 6, depositing a layer ofinsulating material for STI regions 104 on protective layer 636,annealing of the layer of insulating material, chemical mechanicalpolishing (CMP) the annealed layer of insulating material, and etchingthe polished structure to form the structure of FIG. 7. The protectivelayer 636 may include a nitride material (e.g., SiN) and may bedeposited using, for example, ALD or CVD. Protective layer 636 may helpto prevent oxidation of fin structures 106 during the annealing processof the layer of insulating material.

In some embodiments, the layer of insulating material may include, forexample, silicon oxide, silicon nitride, silicon oxynitride,fluoride-doped silicate glass (FSG), or a low-k dielectric material. Insome embodiments, the deposition of the layer of insulating material maybe performed using any deposition methods suitable for flowabledielectric materials (e.g., flowable silicon oxide). For example,flowable silicon oxide may be deposited for STI regions 104 using aflowable CVD (FCVD) process. The FCVD process may be followed by a wetanneal process. The wet anneal process may include annealing thedeposited layer of insulating material in steam at a temperature in arange from about 200° C. to about 700° C. for a period in a range fromabout 30 min to about 120 min. The wet anneal process may be followed bythe CMP process that may remove the patterned hard mask layer andportions of the layer of the insulating material to substantiallycoplanarize a top surface of the layer of insulating material with topsurfaces of fin structures 106. The CMP process may be followed by theetching process to etch back the layer of insulating material andprotective layer 636 to form the structure of FIG. 7.

The etch back of the layer of insulating material may be performed, forexample, by a dry etch process, a wet etch process, or a combinationthereof. In some embodiments, the dry etch process may include using aplasma dry etch with a gas mixture having octafluorocyclobutane (C₄F₈),argon (Ar), oxygen (O₂), and helium (He), fluoroform (CHF₃) and He,carbon tetrafluoride (CF₄), difluoromethane (CH₂F₂), chlorine (Cl₂), andO₂, hydrogen bromide (HBr), O₂, and He, or a combination thereof with apressure ranging from about 1 mTorr to about 5 mTorr. In someembodiments, the wet etch process may include using a dilutedhydrofluoric acid (DHF) treatment, an ammonium peroxide mixture (APM), asulfuric peroxide mixture (SPM), hot deionized water (DI water), or acombination thereof. In some embodiments, the wet etch process mayinclude using a CERTAS® etch process that may use ammonia (NH₃) andhydrofluoric acid (HF) as etchants and inert gases such as, for example,Ar, xenon (Xe), He, or a combination thereof. In some embodiments, theflow rate of HF and NH₃ used in the CERTAS® etch process may each rangefrom about 10 sccm to about 100 sccm (e.g., about 20 sccm, 30 sccm, or40 sccm). In some embodiments, the CERTAS® etch process may be performedat a pressure ranging from about 5 mTorr to about 100 mTorr (e.g., about20 mTorr, about 30 mTorr, or about 40 mTorr) and a high temperatureranging from about 50° C. to about 120° C.

In referring to FIG. 4, in operation 415, fin isolation structures areformed on portions of the fin structures. For example, fin isolationstructures 107 (as shown in FIG. 11) may be formed on fin portions 106Bof fin structures 106 as described with reference to FIGS. 8-11. Theformation of fin isolation structures 107 may include selectivelymodifying (e.g., converting and/or oxidizing) one or more portions offin structures 106. In some embodiments, the formation of fin isolationstructures 107 may include selectively modifying (e.g., convertingand/or oxidizing) one or more fin portions 106A of fin structures 106.The selective modification (e.g., conversion and/or oxidization) processmay include depositing a masking layer 840 (shown in FIG. 8) on thestructure of FIG. 7, patterning the structure of FIG. 8 to form anexposed region 944 (shown in FIG. 9), etching exposed portions ofmasking layer 840 through exposed region 942 to form etched fin portions1046 (shown in FIG. 10), and oxidizing the etched fin portions 1046 toform fin isolation structure 107 (shown in FIG. 11).

In some embodiments, masking layer 840 may include nitride material(e.g., SiN) and may be deposited using, for example, ALD or CVD. Maskinglayer 840 may have a thickness ranging from about 2 nm to about 4 nm. Asshown in FIG. 9, a portion of masking layer 840 may be exposed throughan exposed region 944 that may be formed using a patterned photoresistlayer 942. The formation of patterned photoresist 942 may be followed bythe etching process to remove portion of masking layer 840 on finstructures 106A that are exposed through exposed region 944. The etchingprocess may form etched fin portions 1046 as shown in FIG. 10. Theetching process may be a dry etching process (e.g., reaction ionetching), a wet etching process, or a combination thereof. The etchingprocess may be followed by the oxidation process to substantially modify(e.g., convert and/or oxidize) the material (e.g., SiGe) of the etchedfin portions 1046 into an oxide material (e.g., SiO₂ or Ge-doped SiO₂)to form fin isolation structures 107 as shown in FIG. 11.

The oxidation process may include flowing steam on the structure of FIG.10 in a chamber at a temperature ranging from about 400° C. to about500° C. During the oxidation process, etched fin portions 1046 may bemodified (e.g., converted and/or oxidized) to the oxide material fromtheir outer surfaces towards their center until substantially allportions of etched fin portions 1046 may be modified (e.g., convertedand/or oxidized) to the oxide material of fin isolation structures 107.

In referring to FIG. 4, in operation 420, an oxide layer are formed onthe fin structures and the fin isolation structures. For example, alayer of oxide material may be blanket deposited on the structure ofFIG. 11 followed by a high temperature anneal process to form oxidelayer 114* as shown in FIG. 12. FIG. 12 is an isometric cut view of thestructure of FIG. 11 along line D-D after the deposition of layer ofoxide material. The layer of oxide material may include, for example,silicon oxide and may be formed by CVD, atomic layer deposition (ALD),plasma enhanced ALD (PEALD), physical vapor deposition (PVD), e-beamevaporation, or other suitable process. In some embodiments, the layerof oxide material may be deposited using PEALD at an energy ranging fromabout 400 W to about 500 W and at a temperature ranging from about 300°C. to about 500° C. The deposition of the layer of oxide material may befollowed by a high temperature anneal process. In some embodiments, thestructure of FIG. 12 after the deposition of the layer of oxide materialmay be subjected to a dry anneal process under oxygen gas flow at atemperature ranging from about 800° C. to about 1050° C.

In referring to FIG. 4, in operation 425, a polysilicon structure andepitaxial regions are formed on the fin structures and spacers areformed on sidewalls of the polysilicon structures. For example,polysilicon structure 1350, spacers 120, and epitaxial regions 108 maybe formed as shown in FIG. 13. Polysilicon structure 1350 may be formedon the structure of FIG. 12. In some embodiments, a vertical dimensionof polysilicon structure 1350 may be in a range from about 90 nm toabout 200 nm. In some embodiments, polysilicon structure 1350 and hardmask layers 1352 and 1354 may be replaced in a gate replacement processduring subsequent processing to form gate structures 110 discussedabove.

In some embodiments, polysilicon structure 1350 may be formed by blanketdeposition of polysilicon, followed by photolithography and etching ofthe deposited polysilicon. The deposition process may include chemicalvapor deposition (CVD), physical vapor deposition (PVD), atomic layerdeposition (ALD), other suitable deposition methods, or a combinationthereof. Photolithography may include photoresist coating (e.g., spin-oncoating), soft baking, mask aligning, exposure, post-exposure baking,developing the photoresist, rinsing, drying (e.g., hard baking), othersuitable processes, or a combination thereof. Etching processes mayinclude dry etching, wet etching, and/or other etching methods (e.g.,reactive ion etching).

In some embodiments, hard mask layers 1352 and 1354 may be patterned onpolysilicon structure 1350 to protect polysilicon structure 1350 fromsubsequent processing steps. Hard mask layers 1352 and 1354 may includeinsulating material such as, for example, silicon nitride.

The formation of hard mask layers 1352 and 1354 may be followed byformation of spacers 120 on sidewalls of polysilicon structure 1350.Spacers 120 may be selectively formed on sidewalls of polysiliconstructure 1350 and may not be formed on oxide layer 114* (shown in FIG.12). The selective formation of spacers 120 may include a surfacetreatment and a deposition process. The surface treatment may includeexposing oxide layer 114* and polysilicon structure 1350 to an inhibitorto form an inhibiting layer (not shown) on top surface of oxide layer114* and to form a H- or F-terminated surfaces on the sidewalls ofpolysilicon structure 1350. The inhibiting layer may have ahydroxyl-terminated surface. The H- or F-terminated surfaces mayfacilitate the deposition of the material of spacers 120. The surfacetreatment may further include selectively converting thehydroxyl-terminated surface to a hydrophobic surface by including ahydrophobic component (e.g., a component having carbon) to thehydroxyl-terminated surface. The hydrophobic surface may preventdeposition of the material of spacers 120 on oxide layer 114*. Thesurface treatment may be followed by the deposition of the material ofspacer 120.

In some embodiments, the material of spacers 120 may be deposited using,for example, CVD or ALD. The surface treatment may be performed beforeor during the deposition process. The deposition process may be followedby, for example, an oxygen plasma treatment to remove the hydrophobiccomponent and the inhibitor layer on the top surface of oxide layer114*. In some embodiments, spacer 120 may include (i) a dielectricmaterial such as, for example, silicon oxide, silicon carbide, siliconnitride, silicon oxy-nitride, (ii) an oxide material, (iii) an nitridematerial, (iv) a low-k material, or (v) a combination thereof. In someembodiments, oxide layer 114* may include silicon oxide and spacers 120may include silicon nitride.

The selective formation of spacers 120 may followed by formation ofoxide layer 114 (shown in FIG. 13) by etching of oxide layer 114* fromregions that are not covered by polysilicon structure 1350 and spacers120. The etch process may include a wet etch process using, for example,diluted HF.

The etching of oxide layer 114* may be followed by the growth ofepitaxial regions 108 on fin structures 106. In some embodiments,epitaxial regions 108 may be grown by (i) chemical vapor deposition(CVD) such as, for example, by low pressure CVD (LPCVD), atomic layerCVD (ALCVD), ultrahigh vacuum CVD (UHVCVD), reduced pressure CVD(RPCVD), or any suitable CVD; (ii) molecular beam epitaxy (MBE)processes; (iii) any suitable epitaxial process; or (iv) a combinationthereof. In some embodiments, epitaxial regions 108 may be grown by anepitaxial deposition/partial etch process, which repeats the epitaxialdeposition/partial etch process at least once. As discussed above, suchrepeated deposition/partial etch process is also called a “cyclicdeposition-etch (CDE) process.” In some embodiments, epitaxial regions108 may be grown by selective epitaxial growth (SEG), where an etchinggas is added to promote the selective growth of semiconductor materialon the exposed surfaces of fin structures 106, but not on insulatingmaterial (e.g., dielectric material of STI regions 104).

In some embodiments, epitaxial regions 108 may be p-type or n-type. Insome embodiments, epitaxial regions 108 may be of opposite doping typewith respect to each other. In some embodiments, p-type epitaxialregions 108 may include SiGe and may be in-situ doped during anepitaxial growth process using p-type dopants such as, for example,boron, indium, or gallium. For p-type in-situ doping, p-type dopingprecursors such as, but not limited to, diborane (B2H6), borontrifluoride (BF3), and/or other p-type doping precursors can be used. Insome embodiments, n-type epitaxial regions 108 may include Si and may bein-situ doped during an epitaxial growth process using n-type dopantssuch as, for example, phosphorus or arsenic. For n-type in-situ doping,n-type doping precursors such as, but not limited to, phosphine (PH₃),arsine (AsH₃), and/or other n-type doping precursor can be used.

In referring to FIG. 4, in operation 435, the polysilicon structure isreplaced with a gate structure. For example, as shown in FIG. 14, gatestructures 110 may be formed after removing polysilicon structures 1350.In some embodiments, prior to the removal of polysilicon structures1350, ESL 122 and ILD layer 124 may be formed as shown in FIG. 14. Insome embodiments, ESL 122 may include, for example, SiNx, SiON, SiC,SiCN, BN, SiBN, SiCBN, or a combination thereof. In some embodiments,ESL 122 may include silicon nitride formed by low pressure chemicalvapor deposition (LPCVD), plasma enhanced chemical vapor deposition(PECVD), chemical vapor deposition (CVD), or atomic layer deposition(ALD). In some embodiments, ILD layer 124 may include a dielectricmaterial. The dielectric material of ILD layer 124 may be depositedusing a deposition method suitable for flowable dielectric materials(e.g., flowable silicon oxide). For example, flowable silicon oxide maybe deposited for ILD layer 124 using flowable CVD (FCVD).

The removal of polysilicon structure 1350 and hard mask layers 1352 and1354 may be performed using a dry etching process (e.g., reaction ionetching) or a wet etching process. In some embodiments, the gas etchantsused in etching of polysilicon structure 1350 and hard mask layers 1352and 1354 may include chlorine, fluorine, or bromine. In someembodiments, an NH₄OH wet etch may be used to remove polysiliconstructure 1350, or a dry etch followed by a wet etch process may be usedto remove polysilicon structure 1350.

The formation of gate structures 110 may include deposition ofdielectric layer (not shown). Dielectric layer may include silicon oxideand may be formed by CVD, atomic layer deposition (ALD), physical vapordeposition (PVD), e-beam evaporation, or other suitable process. In someembodiments, dielectric layer 122 may include (i) a layer of siliconoxide, silicon nitride, and/or silicon oxynitride, (ii) a high-kdielectric material such as, for example, hafnium oxide (HfO₂), TiO₂,HfZrO, Ta₂O₃, HfSiO₄, ZrO₂, ZrSiO₂, (iii) a high-k dielectric materialhaving oxides of Li, Be, Mg, Ca, Sr, Sc, Y, Zr, Al, La, Ce, Pr, Nd, Sm,Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu, or (iv) a combination thereof.High-k dielectric layers may be formed by ALD and/or other suitablemethods. In some embodiments, dielectric layer 122 may include a singlelayer or a stack of insulating material layers.

The deposition of dielectric layer may be followed by deposition of gateelectrode 118. Gate electrode 118 may include a single metal layer or astack of metal layers. The stack of metal layers may include metalsdifferent from each other. In some embodiments, gate electrode 118 mayinclude a suitable conductive material such as, for example, Ti, Ag, Al,TiAlN, TaC, TaCN, TaSiN, Mn, Zr, TiN, TaN, Ru, Mo, WN, Cu, W, Co, Ni,TiC, TiAlC, TaAlC, metal alloys, and/or combinations thereof. Gateelectrode 124 may be formed by ALD, PVD, CVD, or other suitabledeposition process.

The deposited dielectric layer and gate electrode 118 may be planarizedby a CMP process. The CMP process may coplanarize top surfaces ofdielectric layer and gate electrode 118 with top surface ILD layer 124as shown in FIGS. 11A and 11B.

In referring to FIG. 4, in operation 440, S/D contact structures areformed in S/D contact openings. For example, S/D contact structures 128may be formed in S/D contact openings (not shown) as shown in FIG. 1.The formation of S/D contact structures 128 may include formation of S/Dcontact openings, formation of metal silicide layers 129 and conductiveregions 132 to form the structure as shown in FIG. 1.

S/D contact openings (not shown) may be formed on epitaxial regions 108.The formation of S/D contact openings may include (i) removing portionsof ILD layer 124 overlying epitaxial S/D regions 108 to form etched ILDlayer and (ii) removing portions of ESL 122 underlying the etchedportions of ILD layer 124. The removal of the portions of ILD layer 124may include patterning using photolithography to expose areas on topsurface of ILD layer 124 corresponding to the portions of ILD layer 124that are to be removed. The portions of ILD layer 124 may be removed bya dry etching process. In some embodiments, the dry etching process maybe a fluorine-based process.

The ILD etch process may include two steps. In the first etch step,etching may be performed using CF₄ gas at a flow rate ranging from about50 sccm to about 500 sccm. In the second etch step, etching may beperformed using a gas mixture including C₄F₆ gas at a flow rate rangingfrom about 5 sccm to about 50 sccm, Ar gas at a flow rate ranging fromabout 100 sccm to about 500 sccm, and O₂ gas at a flow rate ranging fromabout 5 sccm to about 50 sccm. In some embodiments, each of the firstand second etch steps may be carried out for a time period ranging fromabout 1 sec to about 60 sec. In some embodiments, each of the first andsecond etch steps may be performed at a temperature ranging from about10° C. to about 100° C., under a pressure ranging from about 3 mTorr toabout 500 mTorr, and at an RF power ranging from about 300 W to about800 W. In some embodiments, the first etch step has a higher etch ratethan the second etch step.

The etching of the portions of ILD layer 124 may be followed by a dryetching of portions of ESL 122 underlying the etched portions of ILDlayer 124. In some embodiments, these portions of ESL 122 may be etchedin two steps. In the first etch step, etching may be performed using agas mixture including difluoromethane (CH₂F₂) gas at a flow rate rangingfrom about 5 sccm to about 50 sccm and carbon tetrafluoride (CF₄) gas ata flow rate ranging from about 10 sccm to about 100 sccm. In the secondetch step, etching may be performed using a gas mixture includingfluoromethane (CH₃F) gas at a flow rate ranging from about 5 sccm toabout 50 sccm, Ar gas at a flow rate ranging from about 100 sccm toabout 500 sccm, and H₂ gas at a flow rate ranging from about 100 sccm toabout 500 sccm. In some embodiments, each of the first and second etchsteps may be carried out for a time period ranging from about 1 sec toabout 60 sec. In some embodiments, each of the first and second etchsteps may be performed at a temperature ranging from about 10° C. toabout 100° C., under a pressure ranging from about 10 mTorr to about 100mTorr, and at an RF power ranging from about 500 W to about 800 W. Insome embodiments, the first etch step has a higher etch rate than thesecond etch step.

In some embodiments, the formation of S/D contact openings may befollowed by formation of metal silicide layers 129 as shown in FIG. 1.In some embodiments, the metal used for forming metal silicides mayinclude Co, Ti, or Ni. The formation of metal silicide layers 129 may befollowed by formation of conductive regions 132. The formation ofconductive regions 132 may include deposition of materials of conductiveregions 132 in S/D contact openings to form the structure as shown inFIG. 1. Blanket deposition of the materials of conductive regions 132may be performed using, for example, PVD, CVD, or ALD. In someembodiments, conductive regions 132 may include a conductive materialsuch as, for example, W, Al, Co, Cu, or a suitable conductive material.

The deposition of the materials of conductive regions 132 may befollowed by a CMP process to coplanarize top surfaces of conductiveregions 132 with top surface of ILD layer 124. In some embodiments, theCMP process, may use a silicon or an aluminum abrasive with abrasiveconcentrations ranging from about 0.1% to about 3%. In some embodiments,the silicon or aluminum abrasive may have a pH level less than 7 for Wmetal in conductive regions 132 or may have a pH level greater than 7for cobalt (Co) or copper (Cu) metals in conductive regions 132.

The above embodiments describe structures and methods for fabricatingfin isolation structures (e.g., fin isolation structures 107) of finFETs(e.g., finFETs 100A and 100B) with fewer process steps than othermethods used in forming fin isolation structures. The example methodsmay form the fin isolation structures without substantially degradingthe structural integrity of fin structures (e.g., fin portions 106A and106B) adjacent to and/or in contact with the fin isolation structures.In some embodiments, the example methods may form the fin isolationstructures without substantially reducing strain in the fin structuresand without adversely affecting the high mobility channel performance ofthe finFETs.

In some embodiments, a method of forming a fin field effect transistor(finFET) on a substrate includes forming a fin structure on thesubstrate and forming a shallow trench isolation (STI) region on thesubstrate. First and second fin portions of the fin structure extendabove a top surface of the STI region. The method further includesoxidizing the first fin portion to convert a first material of the firstfin portion to a second material. The second material is different fromthe first material of the first fin portion and a material of the secondfin portion. The method further includes forming an oxide layer on theoxidized first fin portion and the second fin portion and forming firstand second polysilicon structures on the oxide layer.

In some embodiments, a method of forming a fin field effect transistor(finFET) on a substrate includes forming a fin structure on thesubstrate and oxidizing a fin portion of the fin structure to convert amaterial of the fin portion to an oxide material that is different froma material of other fin portions of the fin structure. The methodfurther includes forming an oxide layer on the oxidized fin portion andthe other fin portions, forming a polysilicon structure on the oxidelayer and replacing the polysilicon structure with a gate structure.

In some embodiments, a fin field effect transistor (finFET) on asubstrate includes a fin structure on the substrate. The fin structurehaving first and second fin portions adjacent to each other. The firstfin portion having a material that is different from an oxide materialof the second fin portion. The finFET further includes an epitaxialregion on the first fin portion an etch stop layer on the epitaxialregion and on the second fin portion. The finFET further includes firstand second gate structures on the first and second fin portions,respectively and a source/drain contact structure on the epitaxialregion.

The foregoing disclosure outlines features of several embodiments sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodimentsintroduced herein. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A semiconductor structure, comprising: a firstfin comprising upper and lower first fin portions, wherein the upperfirst fin portion comprises a first material; an epitaxial region on theupper first fin portion; a second fin adjacent to the first fin andcomprising upper and lower second fin portions, wherein the upper secondfin portion comprises: a first portion comprising the first material andin contact with the lower second fin portion; and a second portioncomprising a third material different from the first and secondmaterials, wherein the second portion is in contact with the lowersecond fin portion; an etch stop layer on the epitaxial region and onthe upper second fin portion; and a gate structure formed on the upperfirst fin portion and the upper second fin portion.
 2. The semiconductorstructure of claim 1, further comprising a shallow trench isolation(STI) region having a top surface.
 3. The semiconductor structure ofclaim 2, wherein the upper first and second fin portions protrude fromthe top surface and the lower first and second fin portions are belowthe top surface.
 4. The semiconductor structure of claim 1, wherein theupper first fin portion has a first vertical dimension and the uppersecond fin portion has a second vertical dimension less than the firstvertical dimension.
 5. The semiconductor structure of claim 1, furthercomprising an insulating layer on sidewalls of the lower first finportion and the lower second fin portion.
 7. The semiconductor structureof claim 1, wherein the upper first fin portion has a first verticaldimension and the upper second fin portion has a second verticaldimension that is substantially the same as the first verticaldimension.
 8. The semiconductor structure of claim 7, wherein the firstand second vertical dimensions are between about 50 nm and about 60 nm.9. The semiconductor structure of claim 1, wherein the upper second finportion has a horizontal dimension between about 5 nm and about 10 nm.10. The semiconductor structure of claim 1, wherein the lower first andsecond fin portions comprise a same material.
 11. A semiconductorstructure, comprising: a shallow trench isolation (STI) region; a firstfin, wherein an upper portion of the first fin protrudes from a topsurface of the STI region and comprises a first vertical dimension; anda second fin adjacent to the first fin, wherein the second fincomprises: a first upper portion protruding from the top surface of theSTI region and under an inter-layer dielectric (ILD) layer, wherein thefirst upper portion comprises a second vertical dimension; and a secondupper portion protruding from the top surface of the STI region andunder a gate electrode, wherein the second upper portion comprises athird vertical dimension that is different from the second verticaldimension.
 12. The semiconductor structure of claim 11, furthercomprising an epitaxial region on the upper portion of the first fin.13. The semiconductor structure of claim 11, wherein the second verticaldimension is less than the third vertical dimension.
 15. Thesemiconductor structure of claim 11, wherein the first and second finscomprise respective first and second lower portions below the topsurface of the STI region, and wherein the first and second lowerportions comprise a same material.
 16. A semiconductor structure,comprising: a shallow trench isolation (STI) region; an inter-layerdielectric (ILD) layer over the STI region; a gate electrode over theSTI region; and a fin, comprising: a first upper portion protruding fromthe top surface of the STI region and under the inter-layer dielectric(ILD) layer, wherein the first upper portion comprises a first verticaldimension; and a second upper portion protruding from the top surface ofthe STI region and under the gate electrode, wherein the second upperportion comprises a second vertical dimension that is different from thefirst vertical dimension.
 17. The semiconductor structure of claim 16,wherein the second vertical dimension is less than the first verticaldimension.
 18. The semiconductor structure of claim 16, wherein thefirst and second upper portions comprise silicon oxide .
 19. Thesemiconductor structure of claim 16, wherein the fin further comprises alower portion below the top surface of the STI region and comprisesilicon.
 20. The semiconductor structure of claim 19, further comprisingan insulating layer on sidewalls of the lower portion.